1. Technical Field
The present invention relates generally to seals for rotary machines and, more particularly, to a seal assembly and rotary machine containing such seal.
2. Related Art
In many rotary machines, such as a gas turbine or jet engine, a gas is compressed in a compressor and mixed with a fuel source in a combustor. The combination of gas and fuel is then ignited for generating combustion gases that are directed to turbine stage(s) that derive energy therefrom. Both turbine stage(s) and compressor have stationary or non-rotating components, e.g., vanes, that cooperate with rotating components, e.g., blades, for compressing and expanding the operational gases. The operational gases change in pressure through the machine and a variety of seals are provided to preserve the differential pressures where necessary to maximize machine efficiency and performance. An exemplary seal may be provided between a turbine rotor and a cooperating stator or stator body so the rotor may be pressurized to provide thrust balance relative to the rearwardly directed force generated by the engine and the forward direction of the engine.
In the above-described settings, turbine components and seals exceed the operating temperature range of flexible organic compound elastomer seals used in lower temperature applications. Accordingly, seals used must be capable of operation in a high temperature environment. In addition, the seals used must address the close operating clearances required in machinery of this type. Rotary machine seal design also requires consideration of the relative motion between components produced by the differential thermal expansion that occurs throughout the machinery operating cycle compared to cold clearance at assembly.
One structure commonly provided to control leakage flow along a turbine shaft or other rotating surface is a labyrinth seal. In this setting, a variety of blocking seal strips and obstructions are used between stationary turbine components. Solid labyrinth seals typically have a relatively large clearance to avoid rub damage. Labyrinth seals, therefore, do not maximize machine performance.
Another commonly used seal is a brush seal, which include a pack of metal bristles that contact a rotor at free ends thereof to maintain a seal with the rotor. The bristles may be inclined relative to the rotor and may be supported by plates. Brush seals have been aggressively pursued in recent years to provide tighter clearances in rotating machinery seal designs because they have some resilience to accommodate rubbing against the rotating component. For instance, in U.S. Pat. No. 5,090,710, issued to Flower, a brush seal is comprised of closely packed fine wires or filaments that are weld assembled in a carrier assembly that is then inserted in a machine with the bristles wiping the rotating surface. The bristles and assembly are fabricated of materials suitable for the fluid temperature and, compared to a labyrinth seal, leakage is reduced through and past the bristles in close contact with the rotating surface.
Brush seals, however, pose a number of deficiencies. First, the multistep brush seal manufacturing process is costly. Second, brush seal bristles do not always maintain a close running clearance because of their inherent inability to withstand long term wear. Third, brush seals exposed to solid particles are subject to erosion or other deterioration. Finally, brush seals are also subject to vibration due to movement of the pressurized fluid being sealed. Therefore, brush seals oftentimes require dampening features.
Another type seal is disclosed in U.S. Pat. Nos. 5,042,823 and 5,071,138, both issued to Mackay et al. These disclosures reveal a laminated finger seal providing a planar array of radially and circumferentially extending fingers separated by gaps. This structure suffers from a number of disadvantages. For instance, each stacked lamination is a solid ring (not segmented) and, therefore, is limited in application to large diameter machines that require installation/replacement without rotor removal. In addition, the finger geometry provided is provided in a substantially radial plane, which may prevent adequate flexure of the fingers.
In view of the foregoing, there is a need in the art for a seal assembly having low cost manufacture and capable of withstanding the operational sensitivities described above.
In accordance with the invention a seal assembly is provided that has a number of seal members or xe2x80x9cleafxe2x80x9d seals. The seal assembly may be manufactured from rolled shim stock using wire electro-discharge manufacturing (EDM) to make narrow, precision slots to produce the desired seal member geometry. The seal members may be angled between their free ends and their fixed ends and may include a support for supporting the angle. The invention provides similar benefits as brush seals and finger seals in rotary machine applications but at lower cost and with more robust attributes. Seal member geometry is engineered with respect to thickness, width, length, and number of members to meet specific application requirements of differential pressure and anticipated differential motion. The support serves to limit member movement in one direction and withstand differential pressure, while force imposed by a rub engagement on a rotating component is reduced with the elastic flexure of the seal assembly. Seal member end geometry may be shaped to provide a precision diameter and may also incorporate geometry for aerodynamic lift that would minimize wear in those rotor seal applications that anticipate a heavy transient rub.
In a first aspect of the invention is provided a seal assembly for sealing against a rotatable component, the seal assembly comprising: a first element including a plurality of spaced seal members having slots therebetween; a second element including a plurality of spaced seal members having slots therebetween; and wherein each seal member is angled between a fixed end and a free end thereof, and the free ends slidably engage the rotatable component to seal thereagainst.
A second aspect of the invention provides a rotary machine comprising: a rotatable component and a non-rotatable component, the components lying about a common axis; a seal assembly between the components, the seal assembly including: a plurality of juxtaposed elements, each element including a plurality of spaced seal members defining slots therebetween, each seal member including an angle disposed between a fixed end and a free end thereof, wherein the free ends slidably engage the rotatable component to seal thereagainst; and a support for supporting the angle of each seal member.
In a third aspect of the invention is provided a method of inhibiting fluid flow through an annular slot defined between a stator body and a rotor received in the stator body, the rotor having a longitudinal axis, the method including the steps of: disposing on the stator body a plurality of arcuate elements each having a band portion and an integral plurality of circumferentially disposed seal members having slots therebetween, wherein the seal members include an angle therein and extend inwardly from the stator body at an angle relative to the longitudinal axis to slidably contact the rotor along a circumference thereof; circumferentially aligning and axially juxtaposing the elements; employing the cooperatively disposed elements to define an annular seal extending between the stator body and the rotor; and inhibiting fluid flow through the annular slot with the annular seal.
In a fourth aspect of the invention is provided a method of fabricating a seal assembly for sealing pressurized chambers of a rotary machine having a stator body and a rotor, the method comprising the steps of: (a) cutting slots axially into an edge of a material to form a plurality of seal members; (b) layering the material; (c) securing the layers of material together; (d) forming an angle in the seal members; and (e) coupling the layers of material to a holder that is adapted to be coupled to a stator body of the rotary machine, whereby the seal members slidably engage the rotor of the rotary machine, when in operation, to seal the pressurized chambers.
The foregoing and other features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention.